The efficiency of a centrifugal pump affects the resulting energy and life cycle costs of a pumping system. For this reason, one of the solutions to the energy efficient operation of a pumping system is to maintain the pump in a good mechanical condition, so it could operate at its maximum possible efficiency. This should also ensure that the pump performance (e.g., the produced head H curve as a function of flow rate Q) stays constant.
Over time, the pump efficiency may decrease, for example, because of mechanical wear of the impeller and increased clearances inside the pump (e.g. between the casing and the impeller). In practice, mechanical wear of a centrifugal pump has a decreasing effect on the head H and the flow rate Q that a pump can produce at a constant rotational speed and in constant process conditions (e.g., the pump operating location is changed only because of the changed pump characteristics). Therefore, the wear-related efficiency decrease of a centrifugal pump can be detected by monitoring at least one of these variables in constant process conditions. If the process conditions do not remain constant, the pump operating point location can have several locations, which is why at least two variables should be known to detect the performance decrease in the pump. In the case of variable-speed-driven pumps, the head or flow rate decrease of a centrifugal pump can be compensated by increasing the pump rotational speed, which could also be utilised as a feature of performance decrease in a centrifugal pump.
Known systems for determining wear of a pump include thermodynamic efficiency measurements of the pump, direct measurements of the head, flow rate and shaft power consumption for determining the efficiency of the pump. These known systems can involve shutting the pump and thus the process and/or permanent installations of additional sensors.